Technique for radio transmission under varying channel conditions

ABSTRACT

A technique for radio transmitting data is described. As to a method aspect of the technique data to be transmitted to a receiver is represented by at least two partial modulation symbols. Each of the at least two partial modulation symbols is associated to a different layer of the radio transmission to the receiver. A modulation symbol is generated by combining the at least two partial modulation symbols at different power levels according to the associated layer. The modulation symbol is transmitted to the receiver.

TECHNICAL FIELD

The present disclosure relates to a radio transmission technique. Morespecifically, and without limitation, methods and devices are providedfor transmitting data to a receiver under varying channel conditions.

BACKGROUND

Digital radio communication, including some cellular radio accesstechnologies (RATs), can use shared radio spectrum. An example forshared radio spectrum is includes unlicensed bands such as the 2.45 GHzbands (also referred to as industrial, scientific and medical radiobands or ISM bands) and the 5 GHz bands. Long Term Evolution (LTE)License-Assisted Access (LAA) according to the Third GenerationPartnership Project (3GPP) is an example for a cellular RAT using atleast partly unlicensed bands.

For coexistence on the shared radio spectrum, particularly betweendifferent radio devices using a certain RAT as well as between radiodevices using different RATs, some coexistence mechanism is employed. Acommonly used coexistence mechanism is carrier sense multiple accesswith collision avoidance (CSMA/CA), which is based on a listen beforetalk (LBT) process. Effectively, a radio device that intends to make useof the shared radio spectrum for radio transmission senses a channel tobe used and determines whether the channel is busy (i.e., in use oroccupied) or idle (i.e., unused or unoccupied). If the channel isdetermined to be busy, the radio transmission is deferred, whereas atransmission is initiated if the channel is determined to be idle. Thus,CSMA/CA avoids certain collisions by initiating a transmission only whenthe channel is not already used.

Although this channel access mechanism limits the amount of collisionson the shared radio spectrum, it does not work very well in manysituations. Specifically, the LBT process is performed by the radiodevice intending to initiate a transmission (briefly: transmitter), butthe interference conditions at the radio device intended for thereception (briefly: receiver) may be largely unknown.

In order to indicate varying channel conditions at the receiver to thetransmitter, various implementations of a channel feedback from thereceiver are known. For example, link performance may be optimizedaccording to the standard family IEEE 802.11 (Wi-Fi) by adjusting themodulation and coding scheme (MCS) for the data transmissions based onerror statistics of previously transmitted data packets with the aim toselect an MCS that achieves a sufficiently low error probability and, atthe same time, provides a data rate that is as high as possible. This isan example of link adaptation (LA), which commonly relies on an implicitfeedback such as positive acknowledgment (ACK) or negativeacknowledgment (NACK) for Automatic Repeat reQuest (ARQ), as thereceiver does not provide explicit information about the channelcondition it is experiencing. As an alternative example, which is oftenused in cellular RATs according to 3GPP, the receiver provides explicitfeedback. The explicit feedback may comprise information about theinterference level or an explicit suggestion for a suitable MCS to use.However, irrespectively of whether the feedback is implicit or explicit,to be useful it must allow for prediction of the channel conditions foran upcoming transmission. If the channel conditions vary fast, e.g.based on highly varying interference conditions, any channel feedbackregarding the previous transmission may be essentially useless.

L. Wilhelmsson and J. Persson describe in the document WO 2015/032440 anexplicit indication of the reason for a negative acknowledgment feedback(NACK) to address shortcomings of current channel feedback schemes. Thereason for a decoding failure is explicitly sent to the transmitter,e.g. whether the failure was primarily due to noise or interference.This allows the transmitter to better predict the receiver conditions.However, even if a more suitable MCS can be selected in this way, theselection is still based on long term statistics rather than theinstantaneous channel conditions.

An existing technique that is effective under varying channel conditionsis a hybrid ARQ (HARQ) transmission with incremental redundancyretransmissions. When the receiver conditions are poor, at least someinformation can be extracted at the receiver side, and then aretransmission can be requested as long as the packet has not beensuccessfully decoded. A drawback of HARQ transmission is an increasedcomplexity, both in terms of decoding and in terms of memoryrequirements at the receiver. Yet another drawback is increased latency,especially if more than one retransmission is needed, and potentiallyeven more of a problem if the transmitter needs to contend for thechannel in order to be allowed to transmit on the shared spectrum.

For example, vehicular radio communication using direct sidelinks orbase station connectivity can actively avoid accidents and improvetraffic efficiency if latency is low under rapidly varying channelconditions.

SUMMARY

Accordingly, there is a need for a radio communication technique thatreduces latency, increases reliability and/or increases throughput undervarying channel conditions. Alternatively, or in addition, there is aneed for a radio communication technique that avoids or mitigates theproblem caused by that the interference level at a receiver is very hardto estimate based on the experienced interference level at thetransmitter.

As to a first method aspect, a method of radio transmitting data isprovided. The method may comprise or initiate a step of representingdata to be transmitted to a receiver by at least two partial modulationsymbols. Each of the at least two partial modulation symbols may beassociated to a different layer of the radio transmission to thereceiver. The method may further comprise or initiate a step ofgenerating a modulation symbol by combining the at least two partialmodulation symbols at different power levels according to the associatedlayer. The method may further comprise or initiate a step oftransmitting the modulation symbol to the receiver.

The technique may be implemented as a method of a radio transmittingdata packets, e.g. when a current channel condition and/or a currentreceiver condition (collectively: conditions) are unknown at thetransmitter. The conditions may be unknown in the step of transmittingand/or when formatting the data packet.

Herein, the expression “level” may refer to power on a logarithmicscale, e.g., in relative units such as decibel (dB) or absolute unitssuch as dBm (i.e., dB relative to 1 milliwatt).

The technique may be implemented using a hierarchical modulation in thestep of generating the modulation symbol. For example, referring to thedifferent layers by an integer index, e.g., i=0, 1, . . . , n−1 or 1, 2,. . . , n, the power associated to the respective layers may correspondto a decreasing exponential function of the index, e.g., the power maybe proportional to exp (−i·c) or 2^(−(i·c′)) with some constant c or c′.In other words, referring to the different layers by the integer index,i, the power levels associated to the respective layers may correspondto a decreasing linear function of the index, e.g., the power level maybe −i·C dB with some constant C, relative to the greatest power level.The constant C is an example for a transmission parameter (herein belowbriefly: parameter). By way of example, c=ln 4, c′=2 or C=6 dB.

The combining of the partial modulation symbols may apply suitableparameters such that the receiver is able to decode as many layers asthe channel condition and/or the receiver condition allow.

At least in some embodiments and/or channel conditions, by virtue of thecombined partial modulation symbols (e.g., the hierarchical modulation),the data transmission can be more robust in the presence of noise and/orinterference, e.g., under rapidly fluctuating noise and/or interference.

Embodiments of the technique can enable a preemptive or feedback-lesslink adaptation for the radio transmission of the data to the receiver,e.g., for unicasting to a single receiver or multicasting the same datato several receivers. The different power levels may correspond to thedifferent layers of the radio transmission to the receiver. Depending onthe instant channel conditions at the receiver, more or less of thelayers may be successfully receivable (e.g., decodable) at the receiversolely based on the modulation symbol, i.e., the combined partialmodulation symbols.

The different partial modulation symbols may be combined at thedifferent power levels according to the respective layer. Each layer maybe associated with the corresponding power level. Combining the partialmodulation symbols at different power levels may also be referred to asa hierarchical modulation.

The different layers may enable power-level division multiplexing of thedata for the data transmission to the receiver. The layers may bereferred to as layers of the hierarchical modulation. The power-leveldivision multiplexing may be combined with at least one of time divisionmultiplexing, frequency division multiplexing and spatial divisionmultiplexing (e.g., using antenna division multiplexing, beamformingand/or MIMO channels).

Each of the partial modulation symbols may represent a part of the datato be transmitted to the receiver. Herein, the parts of the datacorresponding to the respective layers and/or the parts of the datarepresented by the respective partial modulation symbols may also bebriefly referred to as the parts of the data.

Preferably, each of the at least two parts of the data represented by arespective one of the at least two partial modulation symbols is to betransmitted to the same receiver. That is, all layers may collectivelyprovide the data to at least one common receiver. For example, the partsof the data represented by the partial modulation symbols are notmultiplexing different streams of data to respectively differentreceivers in one radio resource used by the modulation symbol.

Representing the data by at least two partial modulation symbols maycomprise splitting the data into the two or more parts represented bythe respective partial modulation symbol. For example, a data stream tothe receiver may be split into substreams, e.g., each corresponding to alayer of the radio transmission to the receiver. Each of the substreamsmay be associated with a modulator outputting the respective partialmodulation symbol. For each of the substreams, the part of the data tobe represented by the respective partial modulation symbol may besequentially taken from the respective substream.

All of the at least two parts of the data represented by the respectiveat least two partial modulation symbols may belong to one or more datapackets. Each of the data packets may be addressed to the receiver.

The at least two partial modulation symbols or the at least two parts ofthe data represented by the respective at least two partial modulationsymbols may be non-redundant.

The at least two different partial modulation symbols, which arecombined for generating the modulation symbol, may represent differentparts of the data. The different parts of the data may be completelydisjoint or independent or may overlap at most partially. For example,the different parts of the data may be related solely by the receiverbeing a common addressee of the data.

The parts of the data corresponding to the respective layers of theradio transmission may be independently encoded into codewords. Each ofthe two or more partial modulation symbols may result from therespective codeword according to a modulation scheme.

The codeword may result from applying a channel code to the data. Thechannel code may be a (e.g., linear) block code, a convolutional code, aturbo code, a Viterbi code or a low-density parity-check (LDPC) code.Each of the parts of the data may be encoded downstream of the splittingof the data.

Each of the layers may be associated with a modulator using themodulation scheme for outputting the respective partial modulationsymbol. For example, the codeword of the respective layer may be inputto the associated modulator. Each layer may comprise a processing chainincluding the modulator applying the modulation scheme downstream of anencoder applying the channel code.

Each of the codewords may (e.g., uniquely) represent the respective partof the data. Each of the partial modulation symbols may represent therespective part of the data, e.g., since the partial modulation symbolmay be (e.g., uniquely) representative of the respective codeword.

Parameters of the multi-layer transmission (also: hierarchicalmodulation), e.g., at least one of a number of the layers, themodulation scheme and the encoding, may depend on a channel condition ora receiver condition for the radio transmission to the receiver or anaverage of the conditions (e.g., based on a sequence of reports from thereceiver). While the multi-layer transmission can enable an adaptivedemodulation at the receiver not requiring instant knowledge of thereceiver condition at the transmitter, the parameters may be based on atemporal average of the conditions. There may be no need to know theinstantaneous receiver condition at the transmitter. A time-scale of theaveraging for the parameters may be longer than a time lag inconventional link adaptation (LA) that tracks the channel without orwith shorter temporal averaging.

Each of the partial modulation symbols may represent the respective partof the data using the modulation scheme. Each of the layers may beassociated with a modulator outputting the respective partial modulationsymbol.

The number of the layers, the modulation scheme and/or the encoding(e.g., a modulation and coding scheme, MSC) may be adapted lessfrequently than the duration of the modulation symbol. For example,adapting at least one of the number of the layers, the different powerlevels, the modulation scheme and/or the encoding may be based on areport (e.g., a channel state information, CSI, report) and/or may takethe time of a plurality of modulation symbols. As a numerical example,e.g., while a data packet may have a duration on the order of 1 ms, theparameters for the different layers may be updated based on a channelfeedback every 10 s.

The modulation scheme may comprise at least one of phase shift keying(PSK, particularly quadrature phase shift keying, QPSK), Amplitude ShiftKeying (ASK) and Quadrature Amplitude Modulation (QAM). Differentamplitudes of the QAM may correspond to different power levels that areless than differences between the power levels according to thedifferent layers.

The same modulation scheme may be used for at least two of the partialmodulation symbols combined for generating the modulation symbol. Forexample, each of the at least two partial modulation symbols that arecombined for generating the modulation symbol may use the samemodulation scheme. Alternatively, or in addition, the at least twopartial modulation symbols, which are combined for generating themodulation symbol, may use different modulation schemes.

Alternatively, or in addition, the different layers may use differentchannel codes (e.g., different code rates) for the encoding of the partsof the data (and accordingly for decoding the partial modulation symbolsat the receiver).

Using different modulation schemes (e.g., in the representing step)and/or different coding schemes (e.g., for the encoding) for parts ofthe data corresponding to the different layers may enable a flexible ordynamical adaptation to the variations of the conditions. For example, atransmitter performing the method (or a system comprising thetransmitter and the receiver) may support only two layers. The size ofthe data representable by the modulation symbol, i.e., the size of thefinal modulation alphabet (i.e., the combination of the modulationalphabets of the modulation schemes used at the respective layer for thepartial modulation symbols) may largely vary by combining few differentmodulation schemes at the different layers. For example, the finalsymbol alphabet may achieve a size of 2⁶=64 using QPSK for one layer andusing 16-QAM for another layer.

Each of the at least two partial modulation symbols may comprise atleast one of a phase and an amplitude representing the respective partof the data. The modulation scheme may comprise a set of symbolcandidates (i.e., the modulation alphabet of the respective modulationscheme) for the respective partial modulation symbol, e.g., in aconstellation plane according to a constellation diagram. Each of thesymbol candidates in the set may be different in terms of at least oneof the phase and the amplitude. The partial modulation symbolrepresenting the part of the data may be selected from the set (e.g.,from the constellation diagram) depending on the part of the data.

The step of combining may comprise determining or scaling an amplitudeof the partial modulation symbol according to the respective powerlevel. The different power levels may correspond to scaled modulationalphabets or scaled constellation diagrams. Alternatively or inaddition, the combining may correspond to modulation alphabets orconstellation diagrams shifted in the constellation plane according tothe partial modulation symbol of the next higher layer.

The layers may be ordered according to the respective power levels(e.g., by the integer index). The amplitude of each pair of consecutivelayers may be scaled by a factor of 2 or more, the power of each pair ofconsecutive layers may be different by a factor of 4 or more and/or thepower level of each pair of consecutive layers may be different by 6 dBor more. The different power levels may differ pairwise by 6 dB or more.

The radio transmission may use a channel that is subjected to at leastone of noise and interference. The power levels may be controlled ordetermined depending on an average power of at least one of the noiseand the interference and/or variations (e.g., the variance or size ofthe variations and/or a rate of the variations) of the power of at leastone of the noise and the interference. For example, the average power ofat least one of the noise and the interference may vary over a durationof the modulation symbol by the least power level of the different powerlevels or more. Alternatively, or in addition, the average power of atleast one of the noise and the interference may vary by the least powerlevel of the different power levels or more within a time periodrequired for measuring the channel at the receiver and/or receiving achannel feedback based on the measurement from the receiver for adaptivecoding and/or modulation.

Herein, to “vary by” a certain amount within a certain time mayencompass that the temporal variance over said time is equal to orgreater than the certain amount.

The time-scale of the variations or variance of the conditions may beless than the time-scale for adaptive coding and/or modulation based onthe channel feedback. The channel feedback may comprise at least one ofan implicit feedback and an explicit feedback. The implicit feedback maybe indicative of a result of a previous radio transmission, e.g., apositive or negative acknowledgment feedback for previously transmitteddata. The explicit feedback may be indicative of an average level ofand/or the variations in the noise and/or the interference at thereceiver and/or on the channel. Alternatively, or in addition, theexplicit channel feedback may be indicative of (e.g., a suggestion for)a MCS to use for the data transmission.

The radio transmission may use a channel that is subjected to at leastone of noise and interference. The data or each part of the data maybelong to a data packet. A power of at least one of the noise and theinterference may vary by the least power level of the different powerlevels or more within a time period between subsequently transmitteddata packets.

The variations (e.g., the variance) may or may not be this large all thetime. Some embodiments may beneficially use the technique, e.g. if thepower of at least one of the noise and the interference varies by theleast power level of the different power levels only in some occasionsof the respectively specified time durations or time periods. Forexample, even if the variations from one data packet to the next datapacket may only be 3 dB, a difference of 6 dB for the power levelsbetween layers may still be beneficial (e.g., in terms of throughput),e.g., as compared to a conventionally optimized single-layer modulation.

Alternatively or in addition to determining the power levels associatedwith different layers based on the variations (e.g., the variance) ofthe conditions, the difference between the power levels associated withdifferent layers may be determined by a total range to be covered (e.g.,in terms of transmit power or coverage area) and/or the number of layers(e.g., a maximum number of layers available due to the number ofprocessing chains at the transmitter). For example, the radiotransmission may use a channel that is subjected to at least one ofnoise and interference, and the data may belong to a data packet. Themethod may further comprise or initiate a step of determining at leastone of the number of layers and the different power levels, wherein theleast power level of the different power levels is twice, equal to orless than the power of at least one of the noise and the interference.

The receiver may report (which is also referred to as channel feedback)the channel condition and/or the receiver condition (which is alsoreferred to as conditions) without the need for instant knowledge of theconditions at the transmitter by virtue of the multi-layer transmission.For example, the reported conditions may be time-averaged on anaveraging time-scale and/or the reports may be received with aperiodicity, wherein the averaging time-scale or the periodicity ismultiple times longer than a time-scale of the variations in theconditions at the receiver.

The power of the noise and/or the interference may be measured and/orreported as at least one of a received power (e.g., a reference signalreceived power, RSRP), a received channel power indicator (RCPI), areceived signal strength indicator (RSSI), a signal to noise ratio, SNR,and a signal to noise and interference ratio, SNIR. For example, thenoise power and/or the interference power may fluctuate over a durationof the modulation symbol by at least 2 decibel (dB). The reporting maybe on a time-scale (e.g., the averaging time-scale or the periodicity),which may correspond to the transmission time of a large number ofpackets. For example, the channel feedback from the receiver may bereceived for every 100 packets or 1000 packets.

The data may be transmitted on a channel comprising a plurality ofsubcarriers. The modulation symbol may be transmitted on one of thesubcarriers or each layer may generate a plurality of partial modulationsymbols combined into a respective plurality of modulation symbols, eachbeing mapped to one of the subcarriers. The transmission may comprise aradio transmission.

In a first example, a data packet has a duration of 1 ms. At time t=0,the interference at the receiver may be 10 times weaker than a desiredsignal (i.e., C/I=10 dB). Later, at time t=100 μs, the interference maybe 100 times weaker than the desired signal (i.e., C/I=20 dB). By virtueof the multi-layer transmission more layers may be decodable at thereceiver as compared to a conventional feedback-based LA, because thechanges in C/I are too quick for a feedback-based LA.

In a second example, a data packet has a duration of 1 ms. At time t=0,the interference is as strong as the desired signal (i.e., C/I=0 dB).Later, at time t=100 μs, the interference is 10 times weaker than thedesired signal (i.e., C/I=10 dB). By virtue of the multi-layertransmission more layers may be decodable at the receiver as compared toa convention feedback-based LA because the changes in C/I are too quickfor a feedback-based LA.

Furthermore, the power offsets (i.e., the differences between the powerlevels) in the combined modulation symbol (i.e., for the hierarchicalmodulation) may be the same in the first example and in the secondexample, because the variations in C/I are the same. Still, theinterference may be much stronger in second example. Optionally, thechannel code (e.g., the code rate) used in the first example isdifferent from the channel code used in the second example.

The channel conditions, e.g., the power of at least one of the noise andthe interference, may be unpredictable on a time scale corresponding tothe duration of the modulation symbol or multiples thereof (e.g., asubframe or slot) or the time period between subsequent data packettransmission. By using hierarchical layers (e.g., including a layerhaving a suitable power level corresponding to the noise and/or theinterference), the respective part of the data may be selectivelydemodulated (e.g., and decoded) at the receiver whenever the channelconditions allow.

The combining may comprise coherently adding the at least two partialmodulation symbols at the respective power level according to therespective layer.

The method may further comprise or initiate a step of receiving anacknowledgment feedback indicative of a number of successfully decodedlayers (e.g., the number of demodulated and successfully decoded partialmodulation symbols) based on the transmitted modulation symbol. Theindicated number may be counted starting from the partial modulationsymbol or layer at the highest power level and/or may be further countedin the order of decreasing power levels until (e.g., and including) thepartial modulation symbol or layer at the least power level among thesuccessfully decoded layers.

The acknowledgment feedback may be indicative of the number ofsuccessfully decoded layers. The number may imply a level of noiseand/or interference at the receiver.

The same data may be transmitted to a first receiver and a secondreceiver. The acknowledgment feedback from the first receiver may beindicative of a first number of successfully decoded layers (e.g.,demodulated and successfully decoded partial modulation symbols). Theacknowledgment feedback from the second receiver may be indicative of asecond number of successfully decoded layers (e.g., demodulated andsuccessfully decoded partial modulation symbols) that is different fromthe first number.

A first partial modulation symbol transmitted with a greater power levelthan a second partial modulation symbol may be representative of a firstpart of the data associated with a greater priority or quality ofservice (QoS) than a second part of the data represented by the secondpartial modulation symbol. The data part with greater priority or QoSmay be transmitted or retransmitted on a higher layer in terms of thepower level.

The method may further comprise or initiate a step of transmitting afurther modulation symbol comprising a retransmission of a part of thedata represented by the previously transmitted modulation symbol. Theretransmitted part may be represented by a partial modulation symbol inthe further modulation symbol having a greater power level than thepartial modulation symbol representative of the retransmitted part ofthe data in the previously transmitted modulation symbol. The layer usedfor the retransmission of a part of the data may be increased relativeto the layer used for the same part in the previous transmission withoutincreasing the total power of the retransmission relative to theprevious transmission.

As to a second method aspect, a method of radio receiving data isprovided. The method may comprise or initiate a step of receiving amodulation symbol that is a combination of at least two partialmodulation symbols at different power levels. The method may furthercomprise or initiate a step of demodulating, based on the receivedmodulation symbol, a partial modulation symbol and subtracting thedemodulated partial modulation symbol from the received modulationsymbol resulting in a residual modulation symbol. The method may furthercomprise or initiate a step of repeating the demodulation based on theresidual modulation symbol for demodulating the at least two partialmodulation symbols representing the data.

The partial modulation symbol may be subtracted from the receivedmodulation symbol if and only if the partial modulation symbol has beensuccessfully decoded. Repeating the demodulation may further comprise,e.g., if the demodulated partial modulation symbol is successfullydecoded, subtracting the demodulated partial modulation symbol from theprevious residual modulation symbol. If the demodulation or decodingfails (e.g., at any point be it the first demodulation or a subsequentdemodulation), the subtracting and repeating of the demodulation may beterminated for the received modulation symbol.

The second method aspect may be implemented by a layered decodingapproach at the receiver. Various layers may be decoded one after eachother and/or independently. Moreover, each of the transmitted layers maybe acknowledged separately in the acknowledgment feedback to thereceiver. Alternatively, or in addition, the coding (i.e., the encodingat the receiver and the decoding at the receiver) may be selectedindependently for the different layers (i.e., independent of the otherlayers). The coding may be self-contained for each of the layers. Theparameters (e.g., power levels and/or MCSs) controlling the relativerobustness of the different layers may be adjusted to the expectedvariation (e.g., the variance) in the conditions, e.g., due tointerference or noise.

The received modulation symbol may be successively demodulated (e.g.,and decoded), e.g., layer by layer, by subtracting the demodulated(e.g., and decoded) modulation symbol of the next-higher layer.

The demodulation and/or decoding may be repeated in the order ofdecreasing power levels until the demodulation or the decoding of thedemodulated partial modulation symbol fails. The failure of the decodingmay be determined by an error (e.g., a failed cyclic redundancy check,CRC) when decoding the demodulated partial modulation symbol.

The method may further comprise or initiate a step of transmitting anacknowledgment feedback to a transmitter of the received modulationsymbol, the acknowledgment feedback being indicative of a number ofsuccessfully decoded partial modulation symbols based on the receivedmodulation symbol. The number may correspond to the number ofrepetitions. The number may be counted starting from the partialmodulation symbol at the highest power level and in the order ofdecreasing power levels until the partial modulation symbol at the leastpower level among the successfully decoded partial modulation symbols.

The second method aspect may further comprise any feature, or maycomprise or initiate any step, disclosed in the context of the firstmethod aspect or may comprise a feature or step corresponding thereto.For example, at least two of the partial modulation symbols combined inthe received modulation symbol may correspond to the same modulationscheme applied at different power levels.

Moreover, the first method aspect may be performed at or by atransmitting station (briefly: transmitter), e.g., a base station for adownlink or a radio device for an uplink or a sidelink connection.Alternatively, or in combination, the second method aspect may beperformed at or by a receiving station (briefly: receiver), e.g., a basestation for an uplink or a radio device for a downlink or a sidelinkconnection.

The channel or link used for the data transmission and the radioreception, i.e., the channel between the transmitter and the receivermay comprise multiple subchannels or subcarriers (as a frequencydomain). Alternatively, or in addition, the channel or link may compriseone or more slots for a plurality of modulation symbols (as a timedomain). Alternatively, or in addition, the channel or link may comprisea directional transmission (also: beamforming transmission) at thetransmitter, a directional reception (also: beamforming reception) atthe receiver or a multiple-input multiple-output (MIMO) channel with twoor more spatial streams (as a spatial domain). A modulation symbolaccording to the technique may be transmitted and received for each of aplurality of resource elements defined in at least one of the timedomain, the frequency domain and the spatial domain.

The transmitter and the receiver may be spaced apart. The transmitterand the receiver may be in data or signal communication exclusively bymeans of the radio communication.

In any aspect, the transmitter and the receiver may form, or may be partof, a radio network, e.g., according to the Third Generation PartnershipProject (3GPP) or according to the standard family IEEE 802.11 (Wi-Fi).The radio network may be a radio access network (RAN) comprising one ormore base stations. Alternatively, or in addition, the radio network maybe a vehicular, ad hoc and/or mesh network. The first method aspect maybe performed by one or more embodiments of the transmitter in the radionetwork. The second method aspect may be performed by one or moreembodiments of the receiver in the radio network.

Any of the radio devices may be a mobile or wireless device, e.g., a3GPP user equipment (UE) or a Wi-Fi station (STA). The radio device maybe a mobile or portable station, a device for machine-type communication(MTC), a device for narrowband Internet of Things (NB-IoT) or acombination thereof. Examples for the UE and the mobile station includea mobile phone, a tablet computer and a self-driving vehicle. Examplesfor the portable station include a laptop computer and a television set.Examples for the MTC device or the NB-IoT device include robots, sensorsand/or actuators, e.g., in manufacturing, automotive communication andhome automation. The MTC device or the NB-IoT device may be implementedin a manufacturing plant, household appliances and consumer electronics.

Any of the radio devices may be wirelessly connected or connectable(e.g., according to a radio resource control, RRC, state or active mode)with any of the base stations. Herein, the base station may encompassany station that is configured to provide radio access to any of theradio devices. The base stations may also be referred to as transmissionand reception point (TRP), radio access node or access point (AP). Thebase station or one of the radio devices functioning as a gateway (e.g.,between the radio network and the RAN and/or the Internet) may provide adata link to a host computer providing the data. Examples for the basestations may include a 3G base station or Node B, 4G base station oreNodeB, a 5G base station or gNodeB, a Wi-Fi AP and a network controller(e.g., according to Bluetooth, ZigBee or Z-Wave).

The RAN may be implemented according to the Global System for MobileCommunications (GSM), the Universal Mobile Telecommunications System(UMTS), 3GPP Long Term Evolution (LTE) and/or 3GPP New Radio (NR).

Any aspect of the technique may be implemented on a Physical Layer(PHY), a Medium Access Control (MAC) layer, a Radio Link Control (RLC)layer and/or a Radio Resource Control (RRC) layer of a protocol stackfor the radio communication.

As to another aspect, a computer program product is provided. Thecomputer program product comprises program code portions for performingany one of the steps of the method aspect disclosed herein when thecomputer program product is executed by one or more computing devices.The computer program product may be stored on a computer-readablerecording medium. The computer program product may also be provided fordownload, e.g., via the radio network, the RAN, the Internet and/or thehost computer. Alternatively, or in addition, the method may be encodedin a Field-Programmable Gate Array (FPGA) and/or an Application-SpecificIntegrated Circuit (ASIC), or the functionality may be provided fordownload by means of a hardware description language.

As to a first device aspect, a device for radio transmitting data isprovided. The device may be configured to perform any one of the stepsof the first method aspect. Alternatively, or in addition, the devicemay comprise a representing unit configured to represent data to betransmitted to a receiver by at least two partial modulation symbols.Each of the at least two partial modulation symbols may be associated toa different layer of the radio transmission to the receiver.Alternatively, or in addition, the device may comprise a generating unitconfigured to generate a modulation symbol by combining the at least twopartial modulation symbols at different power levels according to theassociated layer. Alternatively, or in addition, the device may comprisea transmitting unit configured to transmit the modulation symbol to thereceiver.

As to a second device aspect, a device for radio receiving data isprovided. The device may be configured to perform any one of the stepsof the second method aspect. Alternatively, or in addition, the devicemay comprise a receiving unit configured to receive a modulation symbolthat is a combination of at least two partial modulation symbols atdifferent power levels. Alternatively, or in addition, the device maycomprise a demodulating unit configured to demodulate, based on thereceived modulation symbol, a partial modulation symbol and to subtractthe demodulated partial modulation symbol from the received modulationsymbol resulting in a residual modulation symbol. Alternatively, or inaddition, the device may comprise a repeating unit configured to repeatthe demodulation based on the residual modulation symbol fordemodulating the at least two partial modulation symbols representingthe data.

Repeating the demodulation may be implemented by inputting the residualmodulation symbol to the repeating unit, which may output the nextdemodulated partial modulation symbol and a further residual modulationsymbol.

As to a further first device aspect, a device for radio transmittingdata is provided. The device comprises at least one processor and amemory. Said memory may comprise instructions executable by said atleast one processor whereby the device is operative to represent data tobe transmitted to a receiver by at least two partial modulation symbols.Each of the at least two partial modulation symbols may be associated toa different layer of the radio transmission to the receiver. Executionof the instructions may further cause the device to be operative togenerate a modulation symbol by combining the at least two partialmodulation symbols at different power levels according to the associatedlayer. Execution of the instructions may further cause the device to beoperative to transmit the modulation symbol to the receiver. The devicemay be further operative to perform any of the steps of the first methodaspect.

As to a further second device aspect, a device for radio receiving datais provided. The device comprises at least one processor and a memory.Said memory may comprise instructions executable by said at least oneprocessor whereby the device is operative to receive a modulation symbolthat is a combination of at least two partial modulation symbols atdifferent power levels. Execution of the instructions may further causethe device to be operative to demodulate, based on the receivedmodulation symbol, a partial modulation symbol and to subtract thedemodulated partial modulation symbol from the received modulationsymbol resulting in a residual modulation symbol. Execution of theinstructions may further cause the device to be operative to repeat thedemodulation based on the residual modulation symbol for demodulatingthe at least two partial modulation symbols representing the data. Thedevice may be further operative to perform any of the steps of thesecond method aspect.

As to a still further aspect a communication system including a hostcomputer is provided. The host computer may comprise a processingcircuitry configured to provide user data, e.g., depending on thelocation of the UE determined in the locating step. The host computermay further comprise a communication interface configured to forwarduser data to a cellular network for transmission to a user equipment(UE), wherein the UE comprises a radio interface and processingcircuitry, a processing circuitry of the cellular network beingconfigured to execute any one of the steps of the first and/or secondmethod aspect.

The communication system may further include the UE. Alternatively, orin addition, the cellular network may further include one or more basestations and/or gateways configured to communicate with the UE and/or toprovide a data link between the UE and the host computer using the firstmethod aspect and/or the second method aspect.

The processing circuitry of the host computer may be configured toexecute a host application, thereby providing the user data and/or anyhost computer functionality described herein. Alternatively, or inaddition, the processing circuitry of the UE may be configured toexecute a client application associated with the host application.

Any one of the devices, the UE, the base station, the system or any nodeor station for embodying the technique may further include any featuredisclosed in the context of the method aspects, and vice versa.Particularly, any one of the units and modules, or a dedicated unit ormodule, may be configured to perform or initiate one or more of thesteps of the method aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of embodiments of the technique are described withreference to the enclosed drawings, wherein:

FIG. 1 shows an example schematic block diagram of a device for radiotransmitting data;

FIG. 2 shows an example schematic block diagram of a device for radioreceiving data;

FIG. 3 shows an example flowchart for a method of radio transmittingdata, which method may be implementable by the device of FIG. 1;

FIG. 4 shows an example flowchart for a method of radio receiving data,which method may be implementable by the device of FIG. 2;

FIG. 5 shows a schematic block diagram of an embodiment of the device ofFIG. 1;

FIG. 6 schematically illustrates examples for partial modulationsymbols, which may be usable for the methods of FIGS. 3 and 4;

FIG. 7 schematically illustrates an example for a modulation symbolresulting from a combination of partial modulation symbols, which may beusable for the methods of FIGS. 3 and 4;

FIG. 8 schematically illustrates a block error rate of individual layersresulting from an embodiment of the radio devices of FIGS. 1 and 2 inradio communication;

FIG. 9 schematically illustrates a data throughput resulting from anembodiment of the radio devices of FIGS. 1 and 2 in radio communicationas well as a comparative example;

FIG. 10 schematically illustrates embodiments of the radio devices ofFIGS. 1 and 2 in an exemplary hidden-node radio environment;

FIG. 11 schematically illustrates an exemplary radio environmentcomprising spatially distributed interferers;

FIG. 12 schematically illustrates an example of fluctuating levels ofinterference resulting from a trajectory through an exemplary radioenvironment comprising spatially distributed interferers;

FIG. 13 schematically illustrates an example of varying levels of noiseon a long time-scale;

FIG. 14 schematically illustrates an example of varying levels of noiseon an intermediate time-scale;

FIG. 15 schematically illustrates an example of varying levels of noiseon a short time-scale;

FIG. 16 schematically illustrates example measurements of mean andvariance for the levels of noise and interference as quantiles in termsof nodes;

FIG. 17 schematically illustrates further examples of mean and variancefor the levels of noise and interference using the order of nodesdefined for FIG. 16;

FIG. 18 shows an example schematic block diagram of a transmittingstation embodying the device of FIG. 1;

FIG. 19 shows an example schematic block diagram of a receiving stationembodying the device of FIG. 2;

FIG. 20 schematically illustrates an example telecommunication networkconnected via an intermediate network to a host computer;

FIG. 21 shows a generalized block diagram of a host computercommunicating via a base station or radio device functioning as agateway with a user equipment over a partially wireless connection; and

FIGS. 22 and 23 show flowcharts for methods implemented in acommunication system including a host computer, a base station or radiodevice functioning as a gateway and a user equipment.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as a specific networkenvironment in order to provide a thorough understanding of thetechnique disclosed herein. It will be apparent to one skilled in theart that the technique may be practiced in other embodiments that departfrom these specific details. Moreover, while the following embodimentsare primarily described for a New Radio (NR) or 5G implementation, it isreadily apparent that the technique described herein may also beimplemented for any other radio communication technique, including 3GPPLTE (e.g., LTE-Advanced or a related radio access technique such asMulteFire), in a Wireless Local Area Network (WLAN) according to thestandard family IEEE 802.11, for Bluetooth according to the BluetoothSpecial Interest Group (SIG), particularly Bluetooth Low Energy,Bluetooth Mesh Networking and Bluetooth broadcasting, for Z-Waveaccording to the Z-Wave Alliance or for ZigBee based on IEEE 802.15.4.

Moreover, those skilled in the art will appreciate that the functions,steps, units and modules explained herein may be implemented usingsoftware functioning in conjunction with a programmed microprocessor, anApplication Specific Integrated Circuit (ASIC), a Field ProgrammableGate Array (FPGA), a Digital Signal Processor (DSP) or a general purposecomputer, e.g., including an Advanced RISC Machine (ARM). It will alsobe appreciated that, while the following embodiments are primarilydescribed in context with methods and devices, the invention may also beembodied in a computer program product as well as in a system comprisingat least one computer processor and memory coupled to the at least oneprocessor, wherein the memory is encoded with one or more programs thatmay perform the functions and steps or implement the units and modulesdisclosed herein.

FIG. 1 schematically illustrates an example block diagram of a devicefor radio transmitting data. The first radio device is genericallyreferred to by reference sign 100.

The device 100 comprises a modulation module 102 that represents data tobe transmitted to a receiver by at least two partial modulation symbols.Each of the partial modulation symbols is associated to a differentlayer of the radio transmission to the receiver. The device 100 furthercomprises a combination module 104 that generates a modulation symbol bycombining the at least two partial modulation symbols at different powerlevels according to the associated layer. The device 100 furthercomprises a transmission module 106 that transmits the modulation symbolto the receiver.

Any of the modules of the receiving device 100 may be implemented byunits configured to provide the corresponding functionality.

The device 100 may also be referred to as, or may be embodied by, atransmitting station or a transmitter. The device 100 and the receiverare in a radio communication at least for the data transmission at thedevice 100.

FIG. 2 schematically illustrates an example block diagram of a devicefor radio receiving data. The device is generically referred to byreference sign 200.

The device 200 comprises a reception module 202 that receives amodulation symbol. The modulation symbol is a combination of at leasttwo partial modulation symbols at different power levels. The device 200further comprises a demodulation module 204 that demodulates, based onthe received modulation symbol, a partial modulation symbol. The device200 further comprises a subtraction module 206 that subtracts thedemodulated partial modulation symbol from the received modulationsymbol resulting in a residual modulation symbol. The demodulationmodule 204 and the subtraction module 206 may be coupled to repeat thedemodulation based on the residual modulation symbol for demodulating(e.g., one after another or each of) the at least two partial modulationsymbols representing the data.

Any of the modules of the device 200 may be implemented by unitsconfigured to provide the corresponding functionality.

The device 200 may also be referred to as, or may be embodied by, areceiving device or a receiver. The device 200 and a transmitter of thedata are in a radio communication at least for the data reception at thedevice 200.

FIG. 3 shows an example flowchart for a method 300 of radio transmittingdata. The method 300 comprises or initiates a step 302 of representingdata to be transmitted to a receiver by at least two partial modulationsymbols, each associated to a different layer of the radio transmissionto the receiver. The method 300 further comprises or initiates a step304 of generating a modulation symbol by combining the at least twopartial modulation symbols at different power levels according to theassociated layer. The method 300 further comprises or initiates a step306 of transmitting the modulation symbol to the receiver.

The method 300 may be performed by the device 100. For example, themodules 102, 104 and 106 may perform the steps 302, 304 and 306,respectively.

FIG. 4 shows an example flowchart for a method 400 of radio receivingdata. The method 400 comprises or initiates a step 402 of receiving amodulation symbol that is a combination of at least two partialmodulation symbols at different power levels. The method 400 furthercomprises or initiates a step 404 of demodulating, based on the receivedmodulation symbol, a partial modulation symbol and subtracting thedemodulated partial modulation symbol from the received modulationsymbol resulting in a residual modulation symbol. The method 400 furthercomprises or initiates a step 406 of repeating the demodulation 404based on the residual modulation symbol for demodulating 404 (and whereapplicable for subtracting) the at least two partial modulation symbolsrepresenting the data.

The method 400 may be performed by the device 200. For example, themodules 202, 204 and 206 may perform the steps 402, 404 and 406,respectively.

The technique may be applied to uplink (UL), downlink (DL) or directcommunications between radio devices, e.g., device-to-device (D2D)communications or sidelink communications.

Each of the device 100 and the device 200 may be a radio device and/or abase station. Herein, any radio device may be a mobile or portablestation and/or any radio device wirelessly connectable to a base stationor RAN, or to another radio device. A radio device may be a userequipment (UE), a device for machine-type communication (MTC) or adevice for (e.g., narrowband) Internet of Things (IoT). Two or moreradio devices may be configured to wirelessly connect to each other,e.g., in an ad hoc radio network or via a 3GPP sidelink connection.Furthermore, any base station may be a station providing radio access,may be part of a radio access network (RAN) and/or may be a nodeconnected to the RAN for controlling radio access. Further a basestation may be an access point, for example a Wi-Fi access point.

According to the method 300 for the radio transmission of the data, thedata may be transmitted using multiple layers, wherein a robustness ofthe different layers is different. Alternatively, or in addition, eachof the layers may be at least one of individually decoded andindividually acknowledged.

The method 300 may be selectively performed. The transmitter 100 mayselect to use or to turn off feature or steps for transmitting the datausing different layers. E.g., instead of the steps 302 and 304, the datato be transmitted may be represented by a single modulation symbol thatis transmitted in the step 306 to the transmitter, i.e. the data istransmitted using a single layer.

The transmitter 100 may transmit data to two or more devices. The datamay be transmitted to one receiver and at least one further receiver.That is, the data is transmitted using multi-layer transmission 306 toat least one of the devices. Optionally, the data is transmitted using asingle layer to at least another one of the devices.

The selection of whether to perform multi-layer transmission 306 or asingle transmission may be based on how much the channel conditionsand/or receiver conditions (collectively: conditions) are known orexpected to vary, e.g., based on channel feedback. The multi-layertransmission may be selected in case the conditions are expected to varymore than a certain amount, e.g. a predefined or preconfigured thresholdvalue. A single layer transmission may be selected if the conditions areexpected to vary less than a certain amount, e.g. a predefined orpreconfigured threshold value.

The variations (e.g., the variance) may be due to varying interferenceconditions and/or noise conditions at the receiver 200 and/or on thechannel. These conditions may or may not be measurable at thetransmitter 100, e.g., in a hidden-node situation.

The variations may be due to at least one of the receiver and/or thetransmitter moving in the radio network, e.g., at a velocity above apredefined or preconfigured threshold value.

Transmission parameters may comprise the different power levelsassociated to the different layers or the differences betweenneighboring power levels. The (e.g., relative) robustness of the layersmay be defined by the respectively associated power levels (e.g.,applied in the step 304 for the respective layer), a modulation scheme(e.g., applied in the step 302 for the respective layer) and/or a codingscheme (e.g., applied in the step 302 for the respective layer).

The transmission parameters, e.g., the robustness, may be controlledbased on how much the conditions are known or expected to vary. Therelative robustness may be controlled by applying a power level offsetto the different layers.

Alternatively, or in addition, the relative robustness may be controlledby applying an error-correcting coding with different robustness to thedifferent layers. The different robustness of the error-correctingcoding may be achieved by using error-correcting codes of different coderates.

The difference in robustness of the most robust layer and the leastrobust layer may be related to the known or expected variation of theconditions.

In any embodiment, the different parts of the data to be transmitted maybe associated to different priorities and/or different data packets. Therespective priority or data packet may determine the layer (i.e., therelative power level) to be used for the respective part of the data(i.e., for the respective partial modulation symbol representing saidpart of the data). Alternatively, or in addition, which layer to use fora certain part of the data may depend on how many times said part hasbeen retransmitted (e.g., how many times a corresponding data packetcomprising said part of the data has been retransmitted).

FIG. 5 shows a schematic block diagram for an embodiment of thetransmitter 100. Optionally, the data 502 to be transmitted in the step306 may be split at reference sign 504 into the parts 506 of the dataassociated to the different layers 500. Alternatively, or in addition, ahigher protocol layer of a protocol stack at the transmitter 100 mayprovide the different parts 506 separately. For example, the differentparts 506 may correspond to different data streams, different datapackets and/or different HARQ entities.

A typical procedure when transmitting information (i.e., the data 502)is that the information is encoded by an error-correcting encoder 508.The resulting coded bits 510 (also: codeword) are modulated using asuitable modulation scheme 512 (also: modulation format). Theerror-correcting code 508 may, for instance, be a binary convolutioncode (BCC) or a low-density parity check (LDPC) code. Examples for themodulation schemes 512 may comprise phase shift keying (PSK) or M-aryquadrature amplitude modulation (M-QAM).

In the embodiment of FIG. 5, two or more encoders 508 and two or moremodulators 512 are used in parallel, e.g., one encoder 508 and onemodulator 512 in association with each layer 500. The encoders 508 andmodulators 512 may embody the modulation module 102 performing the step302. The output of the different modulators 512, i.e., the partialmodulation symbols 514, are combined by a mapper 516 into a singlesymbol, i.e., the modulation symbol 518, according to the step 304. Themapper 516 may embody the combination module 104. The mapper 516 may addthe partial modulation symbols 514 in a digital domain or may beimplemented by a signal combiner. Both implementations may take theassociated power level into account, e.g., as scaling factors or gain,when combining the partial modulation symbols 514.

The schematically illustrated block diagram for an embodiment of thetransmitter 100 depicted in FIG. 5 can be modified in many ways. Forexample, in this illustrated embodiment, there are three layers 500,while variants of the embodiment may comprise 4 or more layers 500 oronly two layers 500. Furthermore, while the embodiment in FIG. 5 hasseparate processing chains for each layer 500, in a variant of theembodiment, some of the components 508 and/or 512 are shared between thedifferent layers 500. For example, some components 508 and/or 512 may betime-shared or sequentially applied to the different layers.

As a non-limiting example, each layer 500 in the embodiment of FIG. 5 ismodulated using QPSK, i.e., each part 506 of the data 502 comprises twobits of the information or data 502. The three QPSK streams comprisingthe respective partial modulation symbols 514 are then combined by themapper 516 into the modulation symbol 518, i.e., 6 bits of informationin total for the three layers 500.

While features of an embodiment of the transmitter 100 have beendescribed with reference to FIG. 1 and/or FIG. 5, an embodiment of thereceiver 200 may comprise the same features or corresponding features.

To further illustrate how embodiments of the transmitter 100 work,example modulation schemes 512 (e.g., for the three layers 500) aredepicted in FIG. 6. The black dots represent the symbol alphabet in thecomplex plane or constellation plane 600. That is, each dot is aconstellation point or candidate for the partial modulation symbol 514depending on the respective part 506 of the data 502.

All layers 500 shown in FIG. 6 are using QPSK as the modulation scheme512, but the different layers 500 are allocated or associate withdifferent (e.g., relative) power levels. Layer 500 with index i=1 isallocated the most power (i.e., the greatest power level), layer 500with index i=2 is allocated the second most power or the second leastpower, and layer 500 with index i=3 is allocated the least amount ofpower (i.e., the least power level). As illustrated with reference tothe examples for the modulation schemes 512 and symbol alphabets in FIG.6, the symbol alphabet may already take the power level of theassociated layer 500 into account, so that no further weighting orscaling is necessary when the partial modulation symbols 514 arecombined.

The three layers 500 may be then combined in the step 304 by means ofsuperposition, i.e., the combined constellation point of the modulationsymbol 518 finally transmitted in the step 306 is the sum of theconstellation points for the respective partial modulation symbols 514of the three layers 500.

FIG. 7 schematically illustrates an example implementation of thecombining step 304. Combining the three layers i=1, 2 and 3, eachcarrying n_(i) bits as the respective part 506 of the data 502,generates in the step 304 one out of 2^((n1+n2+n3)) possible modulationsymbols 518.

The four candidates of layer i=1 are illustrated, wherein the circleindicating the candidate in the first quadrant is not filled, whereasthe other candidates of the layer i=1 are represented by filled circles.In this case, it is the candidate indicated by the non-filled circlethat is transmitted by the layer i=1, i.e., the partial modulationsymbol 514 of the layer i=1. In an analogous manner, the four candidatesof the layer i=2 are also illustrated, centered around (i.e., shiftedto) the non-filled point of the layer i=1 to indicate that the candidateto eventually be transmitted is obtained by adding the vectorsrepresenting the partial modulation symbols 514 of the respective layers500. Also, for the layer i=2, it is the candidate indicated by thenon-filled circle in the first quadrant that is transmitted, i.e., thatis the partial modulation symbol 514 of the layer i=2. The QPSK signal,i.e., the partial modulation symbol 514, corresponding to the layer i=3is depicted with a center of gravity around or origin at the (e.g.,previously shifted) partial modulation symbol 514 of the layer i=2. Forthe layer i=3, all candidates of the respective partial modulationsymbol 514 are indicated by filled circles.

Referring to the example shown in FIG. 7, it is readily seen that thelayer i=1 is more robust than the layer i=2, which in turn is morerobust than the layer i=3. Furthermore, the skilled person appreciatesthat the relative robustness for the different layers 500 may beadjusted as found appropriate, e.g., responsive to a channel feedbackindicative of variations in channel conditions and/or receiverconditions.

As an example, further referring to FIG. 7, by letting the powers of thelayer i=2 and the layer i=3 be very small compared to the power used forthe layer i=1, the resulting signal constellation can be made to almostlook like QPSK, and consequently the performance for Layer 1 would besimilar to that of QPSK, whereas the performance (e.g., an individualsymbol error rate) for the layer i=2 and the layer i=3 would besubstantially susceptible to the current level of noise and/orinterference, e.g., would be substantially worse depending on thecurrent level of noise and/or interference.

Conversely, the transmitter 100 may apply a power offset that isrelatively small (compared to the greatest power level associated to thelayer i=1) in order to obtain decent performance for the less robustlayers i=2 and i=3. In case of such transmission parameters, theperformance for the layer i=1 would be somewhat degraded.

This trade-off between the robustness of the different layers 500 may bevisualized in FIG. 7 by, e.g., considering what amount of induced noiseor interference it takes to cause a demodulation error for one of thepartial modulation symbols of the different layers 500.

FIG. 8 shows example graphs 802 resulting from a numerical simulation oflink performance 800, namely, the symbol error rate or block error rate(BLER on the vertical axis) for each of the layers i=1, i=2 and i=3,respectively, as well as a corresponding performance 850 forconventional 64-QAM with the same BCC, as a function of thesignal-to-noise ratio (SNR on the horizontal axis).

To appreciate the potential gain that can be achieved by embodiments ofthe technique, some simulations were performed. A transmitter 100structured as the one depicted in FIG. 5 was implemented. Theerror-correcting code 508 was a BCC with a memory (or memory order)being 6 and a code rate being 3/4. The relative power offset between thedifferent layers was set to −C=6 dB, i.e., the layer i=2 was 6 dBstronger than the layer i=3 and the layer i=1 was 6 dB stronger than thelayer i=2. The results are shown in FIG. 8.

Referring to FIG. 8, e.g. at a BLER of 1%, it is observed that the layeri=1 is about 3 dB more robust than conventional 64-QAM, the layer i=2 isslightly more robust (e.g., 0.2 dB to 0.3 dB), whereas the layer i=3 isabout 1.5 dB worse.

FIG. 9 shows an example performance 900 in terms of the data rate (orthroughput) as a function of the SNR. More specifically, FIG. 9 shows agraph for the sum 902 of the data rates that is collectively obtained bythe three layers 500. FIG. 9 further shows a graph 950 of the data rateachieved by using conventional 64-QAM as a comparative example. Based ona comparison of the total data rate 902 and the conventional data rate950, one or two threshold values for selectively performing themulti-layer transmission 306 or a single-layer transmission may bedetermined, i.e. which one is the better of the two transmission modes.

In the example illustrated in FIG. 9, for a SNR lower than 15 dB, themulti-layer transmission is preferred. If the SNR is between 15 dB and19 dB, using conventional 64-QAM gives better throughput 950. For a SNRgreater than 19 dB, the performance is the same as both transmissionmodes achieved essentially error-free communication.

An implementation of the method 400 at the receiver 200 used to obtainthe performance shown in FIG. 8 is based on successive interferencecancellation (SIC), i.e., subtraction of the respectively demodulatedpartial modulation symbol 514, according to the steps 404 and 406. Thedifferent layers 500 are decoded one after another starting with thelayer i=1 and continuing with the layer i=2, etc.

While the technique has been described using SIC at the receiver 200,the technique is applicable not only when the receiver 200 is based onSIC, but also if simpler or more complex algorithms are used. Examplesof simpler algorithms include decoding the each of the different layers500 without using any information from the other layers 500. Examples ofmore complex algorithms include jointly decoding all layers 500.

For example, the two or more layers (e.g., the 3 layers in aboveembodiment) may be jointly demodulated. The respective codewords (e.g.,soft bits or hard bits) resulting from the demodulation may be decodedindependently for each of the layers. That is, hard or soft bits for alllayers may be jointly derived from the samples of the receivedmodulation symbol 518. The hard or soft bit calculation uses the factthat the sample of the received modulation symbol 518 is thesuperposition of the partial modulation symbols 514. The procedure ofestimating hard bits comprises hypothesizing the transmitted bits ineach layer 500. Based on each hypothesis, a hypothesis of the partialmodulation symbol is generated according to the modulation scheme 512for each layer 500 and a combined modulation symbol (i.e., a hypothesisof the transmitted modulation symbol 518) is generated (e.g., accordingto the mapper 516). A received signal of the received modulation symbol518 (preferably after equalization, i.e., removing the effect of thechannel) is compared to the hypothesized combination of partialmodulation symbols (i.e., a hypothesis of the transmitted modulationsymbol 518). Hard bit decisions correspond to a hypothesis of the databits that yields a combined modulation symbol that is closest (e.g., inEuclidean distance) to the equalized received signal. The calculation ofsoft bits is similar, but for each data bit, a reliability value (e.g.,a log-likelihood) is computed, e.g., by methods well-known in the art.The hard or soft bits from each layer 500 are then fed to thecorresponding decoders. Decoding is performed independently for eachlayer 500.

At first glance, it might seem that a comparison (as the one presentedin FIG. 9) between a transmission using multiple layers 500 and a fixedsingle-layer transmission is not realistic, because a practical systemusing single-layer transmission would typically perform link adaptation(LA) and, therefore, would not use the conventional 64-QAM when the SNRis below, say, below 15 dB. However, a problem associated with LA forsingle-layer transmission is that LA assumes stable channel conditionsin order to work properly.

FIG. 10 schematically illustrates an exemplary deployment of thetechnique in an exemplary Wi-Fi radio environment 1000 comprising twobasic service sets (BSSs) 1001 and 1002 using shared radio spectrum forillustrating a scenario with varying levels of interference.

While a channel access mechanism (e.g., CSMA/CA) may reduce theoccurrence of collisions on the shared radio spectrum, there are manysituations in which it does not work very well. An example situation isthe so-called hidden node problem, since a listen before talk (LBT)process performed by the radio device intended to initiate atransmission is without knowledge of the current interference conditionsat a radio device intended for the reception. An example of such asituation is illustrated in FIG. 10. An Access Point labeled AP1 mayembody the transmitter 100, which is not within the coverage area of anyof the devices belonging to BSS 1002, so if AP1 has data 502 to transmitto a station labeled STA11 embodying the receiver 200, it will initiatea transmission.

As schematically Illustrated in FIG. 10, the STA11 may experience verydifferent interference conditions. More specifically, the receiverconditions at STA11 will severely depend on what transmissions areongoing in the overlapping BSS 1002. If STA22 is transmitting, this maynot impact a transmission to STA11 at all, whereas if STA21 istransmitting a transmission to STA11 may most likely not be correctlyreceived. If AP2 is transmitting, the outcome may in fact depend on towhich STA it is transmitting. For example, if AP2 uses a directionaltransmission toward STA22, little interference may be experienced atSTA11.

As an example, consider a DL transmission in the BSS 1001, i.e., atransmission according to the method 300 performed by the AP1 as thetransmitter 100 and the STA11 performing the method 400 as the receiver200. The experienced SINR at the STA11 embodying the receiver 200 maydepend on the activities in the neighboring BSS 1002 in the followingway:

-   -   SINR=25 dB, when there is no transmission in the BSS 1002    -   SINR=20 dB, when STA22 is transmitting    -   SINR=15 dB, when AP2 is transmitting to STA22    -   SINR=10 dB when AP2 is transmitting to STA21    -   SINR=10 dB when STA21 is transmitting

Assuming that the AP1 embodying the transmitter 100 does not have anyinformation about the activities in the other BSS 1002, a LA mechanismwould not be able to select the best MCS for a specific transmissionusing a single layer. Rather the LA mechanism would converge to an MCSthat gives the best average performance. Thus, one has to trade highthroughput when the channels condition is good (high MCS) with a highprobability of receiving the packet error free (low MCS).

A multi-layer communication according to the methods 300 and 400 mayavoid or mitigate this trade-off, e.g., as a result of the higherthroughput in the case of low SINR illustrated in FIG. 9. Such a casecannot be countered by feedback-based LA, if the interference occursintermittently (i.e., is unpredictable). Furthermore, LA is not atrivial task on its own, and the discussion above highlights that evenif the LA would be ideal, multi-layer transmission may still achieve ahigher total throughput. The gain using multi-layer communication can beeven greater in practical LA implementations, e.g., due to a time lagbetween the conditions indicated by a channel feedback and the currentconditions. The time lag may be caused by the availability of referencesignals on the channel, measurements at the receiver and the channelfeedback based on the measurements.

While embodiments of the technique are illustrated in FIG. 10 for aWi-Fi deployment, same or further embodiments are also applicable to aradio network 1000 using other radio access technologies. For example,the radio network 1000 may comprise areas of RAN coverage. The radionetwork 1000 may comprises a stationary RAN including at least one basestation. Each base station may serve at least one cell. The base stationmay be an evolved Node B (eNodeB or eNB) or a Next Generation Node B(gNodeB or gNB).

For unicast and multicast transmissions of the data, a directional radiocommunication may be beneficial. For example, a directional transmissionfrom the device 100 may improve the data reception at the device 200.Furthermore, a directional reception at the device 200 may improve thedata reception.

Alternatively, or in addition, a directional transmission from thedevice 100 may reduce the interference at other radio devices that arenot target radio devices of the data transmission. Furthermore, adirectional reception at the device 200 may reduce the interferencecaused by other transmissions not targeting the device 200. Thedirectional transmission may be implemented using an antenna array orany other multi-antenna configuration at the device 100. The directionalreception may be implemented using an antenna array or any othermulti-antenna configuration at the device 200.

FIG. 11 schematically illustrates an example deployment of the techniquein an exemplary radio environment 1100 comprising 16 APs 1102. Each ofthe APs 1102 is associated with 10 STAs 1104. Any pair of the APs 1102and the STAs 1104 may embody the transmitter 100 and the receiver 200,respectively, or vice versa.

To illustrate variations that can be experienced in such a deploymentwith considerable interference, one specific link or channel, i.e., aspecific pair of transmitter 100 and receiver 200, was considered andthe highest data rates that can be supported for individual packets weredetermined.

FIG. 12 shows an example how the highest data rate may vary betweentransmitted data packets depending on interference conditions. The datarate (in megabit per second, on the vertical axis) is plotted as afunction of time (e.g., for a plurality of different instants of time onthe horizontal axis). As can be observed, the highest data rate fordifferent packets varies from 6 Mb/s (corresponding to using binaryphase shift keying) to more than 50 Mb/s (corresponding to 64-QAM). Thehighest data rate is determined by the receiver 200 in that it is thereceiver 200 that determines the number of decodable layers.

While the example radio network 1100 in FIG. 11 has been described for aWi-Fi deployment, a similar radio environment may be deployed using a3GPP RAN. More specifically, the radio devices 1104 may comprise 3GPPUEs in a vehicle-to-anything (V2X) radio communication, particularly avehicle-to-vehicle (V2V) radio communication.

The illustration in FIG. 12 shows a substantial variation at the highestdata rate that can be supported. While the result in FIG. 12 is based ona numerical simulation, a very similar behavior can also be seen infield measurements, which is illustrated in the following figures.

FIG. 13 shows an example of measured power 1300 including signal, noiseand interference in unlicensed 2.45 GHz band (Channel 11). That is, theentire received power is indicated on the vertical axis in terms of aReceived Signal Strength Indicator (RSSI). The captured signal sampleshows an interference floor which varies approximately with a 60 Hzperiodicity, e.g., showing the effects that microwave oven power leakagehas in a 2.45 GHz unlicensed band channel. While this interference isrelatively slow with respect to a length of data packet, e.g. lengths of4 ms according to IEEE 802.11ax, the variations are too fast for afeedback-base LA, e.g., a typical Rate Adaptation Algorithms (RAA) usedby Wi-Fi APs.

The example shown in FIG. 14 shows power 1300 measured in an unlicensed5 GHz band (Channel 148). The measured power 1300 includes signals plusinterference and noise on the 5 GHz channel in an enterprise venue.Wi-Fi 802.11 transmissions are easily visible in the measured power1300. The interference or noise is clearly not additive white Gaussiannoise (AWGN) with constant power, but is time varying.

FIG. 15 shows the measured power 1300 of FIG. 14 in an enlarged timesection (i.e., “zoomed in” on the horizontal axis). The measured power1300 includes several dB of interference floor variations. Thisinterference is somewhat static over the duration of a few microseconds,but varies over the full range of values on the order of tens ofmicroseconds, e.g., on the order of the duration of one modulationsymbol 518.

The interference examples in FIGS. 12 to 15 show conditions under whichembodiments can yield throughput gains over single-layer or non-tieredtransmissions schemes. Taking Wi-Fi as example, the symbol durationaccording to IEEE 802.11ax is typically 13.6 μs (with a small variationdepending on the added CP). While feedback-based LA cannot respondfaster than the packet length, which may be 1 ms, the multi-layercommunication can be robust under such rapidly varying conditions.

Further examples for levels of interference experienced in Wi-Finetworks, e.g., in the unlicensed 2.45 GHz band, are illustrated inFIGS. 16 and 17. The plot 1600 in FIG. 16 show the sampled noise andinterference floor measure at 225 Wi-Fi APs (also: Access Nodes) spreadout across a city. From 9 am to 4 pm, 100 periodic samples were takenfrom each of the 225 Wi-Fi APs. For each AP an average 1602 of the noiseand interference (middle line), a minimum 1604 of the noise andinterference (lower line) and a maximum 1606 of the noise andinterference (upper line) is determined. More specifically, the 225Wi-Fi APs, as plotted in FIG. 16, are ordered from lowest to highestaverage 1602 of the noise and interference.

As an observational result, the Wi-Fi APs experienced noise andinterference with a variation of ±10 dB. The same noise and interferencedata was collected the following day. Using the order for the 225 Wi-FiAPs defined for FIG. 16, the average 1602, the minimum 1604 and themaximum 1606 are plotted in the same order in FIG. 17. As anobservational result, the Wi-Fi APs experienced approximately the sameabsolute interference and variations. This implies that unlicensed bandinterference tends to be location dependent, but still exhibits large±10 dB dynamic changes in absolute interference levels.

In those locations exhibiting interference levels with significantvariability, an implementation of the multi-layer communicationaccording to the methods 300 and 400 can provide significant performanceimprovements. Moreover, high-capacity venues such as stadiums havesimilar and even more extreme variations of noise and interference andcan greatly benefit from an implementation of the multi-layercommunication according to the methods 300 and 400.

Any of the above embodiments for applying the multi-layer communication,e.g., to a link that (potentially) suffers from significant variationsin the experienced receiver conditions, may further comprise any of thefeatures of below implementations.

A first implementation may selectively use the multi-layer transmission.As already discussed, the gain obtained from using multi-layertransmission originates from (e.g., largely) unpredictably varyingchannel conditions and/or receiver conditions (collectively:conditions). When the conditions are not varying, a multi-layertransmission may still be used, but it will typically result in aperformance loss compared to single-layer transmission provided asuitable MCS is found.

This property may be exploited by selectively using the multi-layercommunication. As one example in accordance with the firstimplementation, an AP 100 may use multi-layer transmission to a set ofone or more of its associated STAs at the same time as a single-layertransmission is used for another (e.g., disjoint) set of one or more ofthe associated STAs.

Another example of the first implementation relates to an individuallink or channel. The transmitter 100 may select to change fromsingle-layer transmission to a multi-layer transmission 306 (or viceversa) based on varying conditions. The change may in this case beinitiated either by the transmitter 100 (e.g. based on difficulty inoperating the LA) or it may be initiated by the receiver 200 (e.g.,based on that the receiver 200 has experienced a change in theinterference conditions).

Further examples of the first implementation also cover a change betweensingle-layer transmission and multi-layer transmission based on that thelink or channel is considered to change from being noise-limited tobeing interference-limited (or vice versa). In this case, single-layertransmission may be used when the link or channel is considered to benoise-limited, whereas multi-layer transmission 306 may be used when thelink or channel is considered to be interference-limited.

Same or still further examples of the first implementation compriseselecting either the single-layer transmission or the multi-layertransmission based on the rate of the channel variations, e.g. based ona measured the Doppler shift. In this case, the multi-layer transmission306 may be used when a Doppler shift is determined to be high, e.g.,greater than a certain threshold value, whereas the single-layertransmission is used when the Doppler shift is determined to be belowthe same threshold value.

A second implementation may determine transmission parameters, e.g.,multi-layer parameters. For a multi-layer communication, the differentlayers 500 are given a specific offset of the power level in order todifferentiate and/or define the robustness of the respective layers 500.The choice of the power offset determines how different the robustnessis for the different layers 500. For example, the larger power offsetthe larger the difference in robustness.

The multi-layer communication on a channel enables to effectively spanthe SINR range of the channel and/or the SINR range over which thereceiver conditions are expected to vary. Thus, it may be desirable toselect the power offset such that the range defined by the least powerlevel and the greatest power level depends on the variation (e.g., thevariance) of the conditions.

According to the second implementation applicable to any embodimentand/or the first implementation, the power offset is based at least inpart on the expected variations of the conditions, e.g., such that agreater power offset is selected when the channel variation is expected(e.g., measured or reported) to be large compared to when the channelvariations are expected (e.g., measured or reported) to be small.

As an example of the second implementation, a system comprising anembodiment of the transmitter 100 and an embodiment of the receiver 200may use three layers 500. Responsive to at least one of the transmitter100 and the receiver 200 measuring or estimating that the SINR varieswithin a range of about 10 dB, the power offset between two adjacent (orneighboring) layers 500 may be selected to 5 dB such that power offsetbetween the most robust and the least robust layer 500 corresponds tothe estimated channel variations.

Same or a further example of the second implementation adapts the numberof used layers 500. Specifically, using a greater number of layers 500may be triggered if at least one of the transmitter 100 and the receiver200 measures or estimates that the channel variations are above acertain threshold value (e.g., defined in dB).

A third implementation may change the layer 500 to be used for aretransmitted part 506 of the data, e.g., for a retransmitted datapacket.

Preferably, the multi-layer transmission is not used to transmitdifferent logical streams to respectively different receivers. Rather,is the technique is beneficially applied for supporting differentlogical streams 506 to a certain receiver 200. The streams 506 may beequally important.

Alternatively, or in addition, the multi-layer communication ispreferably not used for broadcasting applications, in which case thereis no feedback channel for the receiver to request a retransmission incase the packet is not correctly received. Rather, the technique isbeneficially applied for the situation that the parts 506 of the data502 transmitted on the respective different layers 500 are acknowledgedby the intended receiver 200. This may be done by transmitting apositive acknowledgment feedback (i.e., an ACK) to the transmitter 100in case of correctly received packet and/or by transmitting a negativeacknowledgment feedback (i.e., a NACK) to the transmitter 100 if thepacket is not correctly received. The NACK may also be implicit, i.e.,when the packet is not correctly received, the absence of an ACK will beinterpreted as a NACK.

According to the third implementation, which is combinable with anyembodiment and the first or second implementation, the property ofdifferent robustness for the different layers is exploited when aretransmission scheme is used. An example of such a retransmissionscheme includes a simple ARQ scheme, e.g. stop-and-want ARQ, Go-back-NARQ or selective-repeat ARQ.

For an ARQ scheme, a data packet that is not correctly received isretransmitted upon request or expiry of a timer. The retransmissionscheme may also be a hybrid ARQ (HARQ) scheme, in which case theretransmission may not necessarily be identical to the first data packettransmission (but rather redundant to the first data packettransmission), and the receiver 200 combines two or more received datapackets in order to extract the information. Examples of HARQ schemesinclude Chase Combining and Incremental Redundancy.

According to the third implementation, a data packet that isretransmitted is transmitted on a more robust layer than a data packetthat is transmitted for the first time. A non-limiting specific exampleis described for three layers 500.

In a first instance of the transmission 306, three data packets (i.e.,Packet₁, Packet₂ and Packet₃) are transmitted for the first time on arespective layer 500, i.e., on Layer₁, Layer₂ and Layer₃, respectively.Based on the one or more modulation symbols 518 of the firsttransmission, the partial modulation symbol 514 of the Layer₁ iscorrectly decoded at the receiver 200, whereas the partial modulationsymbols 514 of the Layer₂ and the Layer₃ are in error.

In a later (e.g., the next) instance of the transmission 306, thetransmitter 100 uses the Layer₁ and the Layer₂ for retransmitting thetwo data packets previously not correctly received at the receiver 200,whereas the Layer₃ is used for transmitting a new data packet. In thiscase, the choice of which data packet to retransmit on the Layer₁ andthe Layer₂ may be arbitrary. Assuming for the purpose of explanation, inthis instant of the transmission 306, only the Layer₁ is correctlyreceived, whereas the Layer₂ and the Layer₃ are in error at the receiver200.

The transmitter 100 is now faced with the situation that one data packethas failed in two transmissions (or has been retransmitted once), onedata packet has failed in one transmission, and there is one new datapacket for transmission to the receiver 200. In this case, thetransmitter 100 transmits the data packet that has failed twice on theLayer₁, the data packet that has failed once on the Layer₂, and the newdata packet on Layer₃.

FIG. 18 shows a schematic block diagram for an embodiment of the device100. The device 100 comprises one or more processors 1804 for performingthe method 300 and memory 1806 coupled to the processors 1804. Forexample, the memory 1806 may be encoded with instructions that implementat least one of the modules 102, 104 and 106.

The one or more processors 1804 may be a combination of one or more of amicroprocessor, controller, microcontroller, central processing unit,digital signal processor, application specific integrated circuit, fieldprogrammable gate array, or any other suitable computing device,resource, or combination of hardware, microcode and/or encoded logicoperable to provide, either alone or in conjunction with othercomponents of the device 100, such as the memory 1806, transmitterfunctionality. For example, the one or more processors 1804 may executeinstructions stored in the memory 1806. Such functionality may includeproviding various features and steps discussed herein, including any ofthe benefits disclosed herein. The expression “the device beingoperative to perform an action” may denote the device 100 beingconfigured to perform the action.

As schematically illustrated in FIG. 18, the device 100 may be embodiedby a transmitting station 1800, e.g., functioning as a transmitting basestation or UE. The transmitting station device 1800 comprises a radiointerface 1802 coupled to the device 100 for radio communication withone or more receiving stations, e.g., functioning as a receiving basestation or UE.

FIG. 19 shows a schematic block diagram for an embodiment of the device200. The device 200 comprises one or more processors 1904 for performingthe method 400 and memory 1906 coupled to the processors 1904. Forexample, the memory 1906 may be encoded with instructions that implementat least one of the modules 202, 204 and 206.

The one or more processors 1904 may be a combination of one or more of amicroprocessor, controller, microcontroller, central processing unit,digital signal processor, application specific integrated circuit, fieldprogrammable gate array, or any other suitable computing device,resource, or combination of hardware, microcode and/or encoded logicoperable to provide, either alone or in conjunction with othercomponents of the device 200, such as the memory 1906, receiverfunctionality. For example, the one or more processors 1904 may executeinstructions stored in the memory 1906. Such functionality may includeproviding various features and steps discussed herein, including any ofthe benefits disclosed herein. The expression “the device beingoperative to perform an action” may denote the device 200 beingconfigured to perform the action.

As schematically illustrated in FIG. 19, the device 200 may be embodiedby a receiving device 1900, e.g., functioning as a receiving basestation or UE. The receiving device 1900 comprises a radio interface1902 coupled to the device 200 for radio communication with one or moretransmitting stations, e.g., functioning as a transmitting base stationor UE.

With reference to FIG. 20, in accordance with an embodiment, acommunication system 2000 includes a telecommunication network 2010,such as a 3GPP-type cellular network, which comprises an access network2011, such as a radio access network, and a core network 2014. Theaccess network 2011 comprises a plurality of base stations 2012 a, 2012b, 2012 c, such as NBs, eNBs, gNBs or other types of wireless accesspoints, each defining a corresponding coverage area 2013 a, 2013 b, 2013c. Each base station 2012 a, 2012 b, 2012 c is connectable to the corenetwork 2014 over a wired or wireless connection 2015. A first userequipment (UE) 2091 located in coverage area 2013 c is configured towirelessly connect to, or be paged by, the corresponding base station2012 c. A second UE 2092 in coverage area 2013 a is wirelesslyconnectable to the corresponding base station 2012 a. While a pluralityof UEs 2091, 2092 are illustrated in this example, the disclosedembodiments are equally applicable to a situation where a sole UE is inthe coverage area or where a sole UE is connecting to the correspondingbase station 2012.

The telecommunication network 2010 is itself connected to a hostcomputer 2030, which may be embodied in the hardware and/or software ofa standalone server, a cloud-implemented server, a distributed server oras processing resources in a server farm. The host computer 2030 may beunder the ownership or control of a service provider, or may be operatedby the service provider or on behalf of the service provider. Theconnections 2021, 2022 between the telecommunication network 2010 andthe host computer 2030 may extend directly from the core network 2014 tothe host computer 2030 or may go via an optional intermediate network2020. The intermediate network 2020 may be one of, or a combination ofmore than one of, a public, private or hosted network; the intermediatenetwork 2020, if any, may be a backbone network or the Internet; inparticular, the intermediate network 2020 may comprise two or moresub-networks (not shown).

The communication system 2000 of FIG. 20 as a whole enables connectivitybetween one of the connected UEs 2091, 2092 and the host computer 2030.The connectivity may be described as an over-the-top (OTT) connection2050. The host computer 2030 and the connected UEs 2091, 2092 areconfigured to communicate data and/or signaling via the OTT connection2050, using the access network 2011, the core network 2014, anyintermediate network 2020 and possible further infrastructure (notshown) as intermediaries. The OTT connection 2050 may be transparent inthe sense that the participating communication devices through which theOTT connection 2050 passes are unaware of routing of uplink and downlinkcommunications. For example, a base station 2012 may not or need not beinformed about the past routing of an incoming downlink communicationwith data originating from a host computer 2030 to be forwarded (e.g.,handed over) to a connected UE 2091. Similarly, the base station 2012need not be aware of the future routing of an outgoing uplinkcommunication originating from the UE 2091 towards the host computer2030.

By virtue of the method 300 and 400 being performed by any one of theUEs 2091 or 2092 and/or any one of the base stations 2012, theperformance of the OTT connection 2050 can be improved, e.g., in termsof increased throughput and/or reduced latency.

Example implementations, in accordance with an embodiment, of the UE,base station and host computer discussed in the preceding paragraphswill now be described with reference to FIG. 21. In a communicationsystem 2100, a host computer 2110 comprises hardware 2115 including acommunication interface 2116 configured to set up and maintain a wiredor wireless connection with an interface of a different communicationdevice of the communication system 2100. The host computer 2110 furthercomprises processing circuitry 2118, which may have storage and/orprocessing capabilities. In particular, the processing circuitry 2118may comprise one or more programmable processors, application-specificintegrated circuits, field programmable gate arrays or combinations ofthese (not shown) adapted to execute instructions. The host computer2110 further comprises software 2111, which is stored in or accessibleby the host computer 2110 and executable by the processing circuitry2118. The software 2111 includes a host application 2112. The hostapplication 2112 may be operable to provide a service to a remote user,such as a UE 2130 connecting via an OTT connection 2150 terminating atthe UE 2130 and the host computer 2110. In providing the service to theremote user, the host application 2112 may provide user data, which istransmitted using the OTT connection 2150. The user data may depend onthe location of the UE 2130 determined in the step 206. The user datamay comprise auxiliary information or precision advertisements (also:ads) delivered to the UE 2130. The location may be reported by the UE2130 to the host computer, e.g., using the OTT connection 2150, and/orby the base station 2120, e.g., using a connection 2160.

The communication system 2100 further includes a base station 2120provided in a telecommunication system and comprising hardware 2125enabling it to communicate with the host computer 2110 and with the UE2130. The hardware 2125 may include a communication interface 2126 forsetting up and maintaining a wired or wireless connection with aninterface of a different communication device of the communicationsystem 2100, as well as a radio interface 2127 for setting up andmaintaining at least a wireless connection 2170 with a UE 2130 locatedin a coverage area (not shown in FIG. 21) served by the base station2120. The communication interface 2126 may be configured to facilitate aconnection 2160 to the host computer 2110. The connection 2160 may bedirect or it may pass through a core network (not shown in FIG. 21) ofthe telecommunication system and/or through one or more intermediatenetworks outside the telecommunication system. In the embodiment shown,the hardware 2125 of the base station 2120 further includes processingcircuitry 2128, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The base station 2120 further has software 2121 stored internally oraccessible via an external connection.

The communication system 2100 further includes the UE 2130 alreadyreferred to. Its hardware 2135 may include a radio interface 2137configured to set up and maintain a wireless connection 2170 with a basestation serving a coverage area in which the UE 2130 is currentlylocated. The hardware 2135 of the UE 2130 further includes processingcircuitry 2138, which may comprise one or more programmable processors,application-specific integrated circuits, field programmable gate arraysor combinations of these (not shown) adapted to execute instructions.The UE 2130 further comprises software 2131, which is stored in oraccessible by the UE 2130 and executable by the processing circuitry2138. The software 2131 includes a client application 2132. The clientapplication 2132 may be operable to provide a service to a human ornon-human user via the UE 2130, with the support of the host computer2110. In the host computer 2110, an executing host application 2112 maycommunicate with the executing client application 2132 via the OTTconnection 2150 terminating at the UE 2130 and the host computer 2110.In providing the service to the user, the client application 2132 mayreceive request data from the host application 2112 and provide userdata in response to the request data. The OTT connection 2150 maytransfer both the request data and the user data. The client application2132 may interact with the user to generate the user data that itprovides.

It is noted that the host computer 2110, base station 2120 and UE 2130illustrated in FIG. 21 may be identical to the host computer 2030, oneof the base stations 2012 a, 2012 b, 2012 c and one of the UEs 2091,2092 of FIG. 20, respectively. This is to say, the inner workings ofthese entities may be as shown in FIG. 21 and independently, thesurrounding network topology may be that of FIG. 20.

In FIG. 21, the OTT connection 2150 has been drawn abstractly toillustrate the communication between the host computer 2110 and the useequipment 2130 via the base station 2120, without explicit reference toany intermediary devices and the precise routing of messages via thesedevices. Network infrastructure may determine the routing, which it maybe configured to hide from the UE 2130 or from the service provideroperating the host computer 2110, or both. While the OTT connection 2150is active, the network infrastructure may further take decisions bywhich it dynamically changes the routing (e.g., on the basis of loadbalancing consideration or reconfiguration of the network).

The wireless connection 2170 between the UE 2130 and the base station2120 is in accordance with the teachings of the embodiments describedthroughout this disclosure. One or more of the various embodimentsimprove the performance of OTT services provided to the UE 2130 usingthe OTT connection 2150, in which the wireless connection 2170 forms thelast segment. More precisely, the teachings of these embodiments mayreduce the latency and improve the data rate and thereby providebenefits such as better responsiveness.

A measurement procedure may be provided for the purpose of monitoringdata rate, latency and other factors on which the one or moreembodiments improve. There may further be an optional networkfunctionality for reconfiguring the OTT connection 2150 between the hostcomputer 2110 and UE 2130, in response to variations in the measurementresults. The measurement procedure and/or the network functionality forreconfiguring the OTT connection 2150 may be implemented in the software2111 of the host computer 2110 or in the software 2131 of the UE 2130,or both. In embodiments, sensors (not shown) may be deployed in or inassociation with communication devices through which the OTT connection2150 passes; the sensors may participate in the measurement procedure bysupplying values of the monitored quantities exemplified above, orsupplying values of other physical quantities from which software 2111,2131 may compute or estimate the monitored quantities. The reconfiguringof the OTT connection 2150 may include message format, retransmissionsettings, preferred routing etc.; the reconfiguring need not affect thebase station 2120, and it may be unknown or imperceptible to the basestation 2120. Such procedures and functionalities may be known andpracticed in the art. In certain embodiments, measurements may involveproprietary UE signaling facilitating the host computer's 2110measurements of throughput, propagation times, latency and the like. Themeasurements may be implemented in that the software 2111, 2131 causesmessages to be transmitted, in particular empty or “dummy” messages,using the OTT connection 2150 while it monitors propagation times,errors etc.

FIG. 22 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 20 and 21. Forsimplicity of the present disclosure, only drawing references to FIG. 22will be included in this section. In a first step 2210 of the method,the host computer provides user data. In an optional substep 2211 of thefirst step 2210, the host computer provides the user data by executing ahost application. In a second step 2220, the host computer initiates atransmission carrying the user data to the UE. In an optional third step2230, the base station transmits to the UE the user data which wascarried in the transmission that the host computer initiated, inaccordance with the teachings of the embodiments described throughoutthis disclosure. In an optional fourth step 2240, the UE executes aclient application associated with the host application executed by thehost computer.

FIG. 23 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 20 and 21. Forsimplicity of the present disclosure, only drawing references to FIG. 23will be included in this section. In a first step 2310 of the method,the host computer provides user data. In an optional substep (not shown)the host computer provides the user data by executing a hostapplication. In a second step 2320, the host computer initiates atransmission carrying the user data to the UE. The transmission may passvia the base station, in accordance with the teachings of theembodiments described throughout this disclosure. In an optional thirdstep 2330, the UE receives the user data carried in the transmission.

Any embodiment or implementation of the receiver may use a layereddecoding approach, i.e., the receiver may start decoding the most robustlayer and if it succeeds, this is beneficial for the other layers as thefirst layer is then subtracted from the received modulation symbol forthe remaining layers. This procedure is then repeated iteratively for aresidual modulation symbol for all remaining layers.

Moreover, the technique may be implemented as a coded system. By way ofexample, a data packet may comprise a plurality of (e.g., on the orderof 1000) coded modulation symbols. Each modulation symbol may resultfrom a combination of three partial modulation symbols, i.e. each havingthree layers. A first implementation of the decoding comprises decodingall partial modulation symbols of layer 1 of the data packet, and thensubtract these and continue with the next layer. A second implementationof the decoding may decide modulation symbol by modulation symbol. Foreach modulation symbol of the data packet, the partial modulationsymbols of layer 1 is demodulated, decoded and subtracted, and so on(based on the residual modulation symbol) for layer 2 and layer 3,before continuing to the next modulation symbol. The performance can bebetter in the first implementation at the cost of a longer delay, sincethe receiver has to effectively take decisions on all 1000 partialmodulation symbols of layer 1 before starting to decode layer 2.

Furthermore, multi-layer modulation parameters may be selected. Theperformance of the more robust layers (e.g., layer associated with thesecond least power level) can become worse if additional layers areadded. Thus, it may be important to not use too many layers. Thetechnique may be implemented to control the parameters of themulti-layer modulation (particularly, the number of layers), e.g.,resulting in improved reliability and/or throughput of the datatransmission.

As has become apparent from above description, embodiments of thetechnique allow for improved spectrum efficiency and reduced delay,e.g., at a very low additional complexity. Moreover, the technique maybe implemented in combination with further coexistence features such astransmission power control (TPC) and beamforming. Furthermore, themulti-layer transmission may be selectively deactivated for a given linkor channel. Alternatively, or in combination, in a given radio network(e.g., within a BSS), the multi-layer transmission may be selectivelyused the radio communication with one or more of the radio devices andnot for the radio communication with other radio devices, which may beimplemented entirely transparent for legacy radio device not supportingthis multi-layer transmission.

Many advantages of the present invention will be fully understood fromthe foregoing description, and it will be apparent that various changesmay be made in the form, construction and arrangement of the units anddevices without departing from the scope of the invention and/or withoutsacrificing all of its advantages. Since the invention can be varied inmany ways, it will be recognized that the invention should be limitedonly by the scope of the following claims.

1. A method of radio transmitting data, the method comprising orinitiating: representing data to be transmitted to a receiver by atleast two partial modulation symbols, each associated to a differentlayer of the radio transmission to the receiver; generating a modulationsymbol by combining the at least two partial modulation symbols atdifferent power levels according to the associated layer; andtransmitting the modulation symbol to the receiver.
 2. (canceled)
 3. Themethod of claim 1, wherein the at least two partial modulation symbolsor the at least two parts of the data represented by the respective atleast two partial modulation symbols are non-redundant.
 4. (canceled) 5.The method of claim 1, wherein at least one of a number of the layers,the modulation scheme and the encoding depends on a channel conditionfor the radio transmission to the receiver. 6.-11. (canceled)
 12. Themethod of claim 1, wherein the radio transmission uses a channel that issubjected to at least one of noise and interference, and wherein atleast one of: a power of at least one of the noise and the interferencevaries over a duration of the modulation symbol by the least power levelof the different power levels or more; a power of at least one of thenoise and the interference varies by the least power level of thedifferent power levels or more within a time period required formeasuring the channel at the receiver and receiving a channel feedbackbased on the measurement from the receiver for adaptive coding and/ormodulation; and/or the data belongs to a data packet, and wherein apower of at least one of the noise and the interference varies by theleast power level of the different power levels or more within a timeperiod between subsequently transmitted data packets. 13.-16. (canceled)17. The method of claim 1, further comprising or initiating: receivingan acknowledgment feedback indicative of a number of successfullydecoded partial modulation symbols based on the transmitted modulationsymbol, the number being counted starting from the partial modulationsymbol at the highest power level and in the order of decreasing powerlevels until the partial modulation symbol at the least power levelamong the successfully decoded partial modulation symbols. 18.(canceled)
 19. The method of claim 1, wherein a first partial modulationsymbol transmitted with a greater power level than a second partialmodulation symbol is representative of a first part of the dataassociated with a greater priority or quality of service, QoS, than asecond part of the data represented by the second partial modulationsymbol.
 20. The method of claim 1, further comprising or initiating:transmitting a further modulation symbol comprising a retransmission ofa part of the data represented by the previously transmitted modulationsymbol, wherein the retransmitted part is represented by a partialmodulation symbol in the further modulation symbol having a greaterpower level than the partial modulation symbol representative of theretransmitted part of the data in the previously transmitted modulationsymbol.
 21. A method of radio receiving data, the method comprising:receiving a modulation symbol that is a combination of at least twopartial modulation symbols at different power levels; demodulating,based on the received modulation symbol, a partial modulation symbol andsubtracting the demodulated partial modulation symbol from the receivedmodulation symbol resulting in a residual modulation symbol; repeatingthe demodulation based on the residual modulation symbol fordemodulating the at least two partial modulation symbols representingthe data.
 22. The method of claim 21, wherein the demodulation isrepeated in the order of decreasing power levels until the demodulationor a decoding of the demodulated partial modulation symbol fails. 23.The method of claim 21, wherein at least two of the partial modulationsymbols correspond to the same modulation scheme applied at differentpower levels.
 24. The method of claim 21, further comprising orinitiating: transmitting an acknowledgment feedback to a transmitter ofthe received modulation symbol, the acknowledgment feedback beingindicative of a number of successfully decoded partial modulationsymbols based on the received modulation symbol, the number beingcounted starting from the partial modulation symbol at the highest powerlevel and in the order of decreasing power levels until the partialmodulation symbol at the least power level among the successfullydecoded partial modulation symbols.
 25. (canceled)
 26. A computerprogram product comprising program code configured to perform operationsof claim 1 when the computer program product is executed on one or morecomputing devices, the computer program product being stored on acomputer-readable recording medium. 27.-30. (canceled)
 31. A device forradio transmitting data, the device comprising: at least one processor;and a memory coupled with said at least one processor, said memorycomprising instructions executable by said at least one processor,whereby the device is operative to, represent data to be transmitted toa receiver by at least two partial modulation symbols, each associatedto a different layer of the radio transmission to the receiver, generatea modulation symbol by combining the at least two partial modulationsymbols at different power levels according to the associated layer, andtransmit the modulation symbol to the receiver.
 32. (canceled)
 33. Adevice for radio receiving data, the device comprising: at least oneprocessor; and a memory coupled with said at least one processor, saidmemory comprising instructions executable by said at least oneprocessor, whereby the device is operative to, receive a modulationsymbol that is a combination of at least two partial modulation symbolsat different power levels, demodulate, based on the received modulationsymbol, a partial modulation symbol and subtracting the demodulatedpartial modulation symbol from the received modulation symbol resultingin a residual modulation symbol, and repeat the demodulation based onthe residual modulation symbol for demodulating the at least two partialmodulation symbols representing the data. 34.-40. (canceled)
 41. Themethod of claim 21, wherein the at least two partial modulation symbolsor the at least two parts of the data represented by the respective atleast two partial modulation symbols are non-redundant.
 42. A computerprogram product comprising program code configured to perform operationsof claim 21 when the computer program product is executed on one or morecomputing devices, the computer program product being stored on acomputer-readable recording medium.
 43. The device of claim 31, whereinthe at least two partial modulation symbols or the at least two parts ofthe data represented by the respective at least two partial modulationsymbols are non-redundant.
 44. The device of claim 31, wherein at leastone of a number of the layers, the modulation scheme and the encodingdepends on a channel condition for the radio transmission to thereceiver.
 45. The device of claim 31, wherein the radio transmissionuses a channel that is subjected to at least one of noise andinterference, and wherein at least one of: a power of at least one ofthe noise and the interference varies over a duration of the modulationsymbol by the least power level of the different power levels or more; apower of at least one of the noise and the interference varies by theleast power level of the different power levels or more within a timeperiod required for measuring the channel at the receiver and receivinga channel feedback based on the measurement from the receiver foradaptive coding and/or modulation; and/or the data belongs to a datapacket, and wherein a power of at least one of the noise and theinterference varies by the least power level of the different powerlevels or more within a time period between subsequently transmitteddata packets.
 46. The device of claim 31, whereby the device is furtheroperative to, receive an acknowledgment feedback indicative of a numberof successfully decoded partial modulation symbols based on thetransmitted modulation symbol, the number being counted starting fromthe partial modulation symbol at the highest power level and in theorder of decreasing power levels until the partial modulation symbol atthe least power level among the successfully decoded partial modulationsymbols.
 47. The device of claim 31, wherein a first partial modulationsymbol transmitted with a greater power level than a second partialmodulation symbol is representative of a first part of the dataassociated with a greater priority or quality of service, QoS, than asecond part of the data represented by the second partial modulationsymbol.
 48. The device of claim 31, whereby the device is furtheroperative to, transmit a further modulation symbol comprising aretransmission of a part of the data represented by the previouslytransmitted modulation symbol, wherein the retransmitted part isrepresented by a partial modulation symbol in the further modulationsymbol having a greater power level than the partial modulation symbolrepresentative of the retransmitted part of the data in the previouslytransmitted modulation symbol.
 49. The device of claim 33, wherein thedemodulation is repeated in the order of decreasing power levels untilthe demodulation or a decoding of the demodulated partial modulationsymbol fails.
 50. The device of claim 33, wherein at least two of thepartial modulation symbols correspond to the same modulation schemeapplied at different power levels.
 51. The device of claim 33, furthercomprising or initiating: transmitting an acknowledgment feedback to atransmitter of the received modulation symbol, the acknowledgmentfeedback being indicative of a number of successfully decoded partialmodulation symbols based on the received modulation symbol, the numberbeing counted starting from the partial modulation symbol at the highestpower level and in the order of decreasing power levels until thepartial modulation symbol at the least power level among thesuccessfully decoded partial modulation symbols.
 52. The method of claim33, wherein the at least two partial modulation symbols or the at leasttwo parts of the data represented by the respective at least two partialmodulation symbols are non-redundant.